Learning Objectives You should learn : About the different types of variables, How to identify them when doing your practical work.

Variables are things that vary and change

Variables In any experiment there are 3 variables: an independent (or input) variable a dependent (or outcome) variable some control variables Let’s look at each type….

3 Kinds of Variables Independent Variable – something that is changed by the scientist What is tested What is manipulated

Independent (input) variable This is the thing that you decide to change. Example 1 Investigating how a weight affects the length of an elastic band. You decide the weight to apply, so: Weight is the independent variable.

3 Kinds of Variables Dependent Variable – something that might be affected by the change in the independent variable What is observed What is measured The data collected during the investigation

Dependent (outcome) variable This is the variable that changes as a result. It is the variable that you measure. Example 1 Investigating how a weight affects the length of an elastic band. You measure the resulting length of the elastic band, so: Length is the dependent variable.

3 Kinds of Variables Controlled Variable – a variable that is not changed Also called constants Allow for a “fair test”

Control variables These are all the variables that must not change, to make sure it is a fair test. Example 1 Investigating how a weight affects the length of an elastic band. You must use the same elastic band all the time, and the same scale etc, so it is a fair test.

same elastic band, same scale, etc, so it is a fair test. In Summary Example 1 The independent variable is ? weight The dependent variable is ? length of the elastic The control variables are ? same elastic band, same scale, etc, so it is a fair test.

I DO Students of different ages were given the same jigsaw puzzle to put together. They were timed to see how long it took to finish the puzzle.

Identify the variables in this investigation.

What was the independent variable? Ages of the students Different ages were tested by the scientist

What was the dependent variable? The time it to put the puzzle together The time was observed and measured by the scientist

What was a controlled variable? Same puzzle All of the participants were tested with the same puzzle. It would not have been a fair test if some had an easy 30 piece puzzle and some had a harder 500 piece puzzle.

WE DO An investigation was done with an electromagnetic system made from a battery and wire wrapped around a nail. Different sizes of nails were used. The number of paper clips the electromagnet could pick up was measured.

What are the variables in this investigation?

Independent variable: Sizes of nails These were changed by the scientist

Dependent variable: Number of paper clips picked up The number of paper clips observed and counted (measured)

Controlled variables: Battery, wire, type of nail None of these items were changed

The higher the temperature of water, the faster an egg will boil. YOU DO The higher the temperature of water, the faster an egg will boil.

Independent variable – temperature of water Dependent variable – time to cook an egg Controlled variable – type of egg

The temperature of water was measured at different depths of a pond. YOU DO The temperature of water was measured at different depths of a pond.

Independent variable – depth of the water Dependent variable – temperature Controlled variable – thermometer

Learning Outcomes You should now: Understand the difference between - independent, - dependent, and - control variables Be able to identify these variables when doing your practical work.